1. Field of the Invention
The present invention generally relates to an industrial vehicle and more particularly, to an industrial vehicle, in which a steering system for steering front and rear wheels in the same direction without restriction to a steering angle and a simply configured differential driving unit are provided, so that a progress direction of the vehicle can be easily changed, and in which a working tool horizontal adjuster and a boom length adjuster are mounted to a boom assembly, and a pivoting unit of an upper frame is mounted to the vehicle, and a leading end of a working tool moves has a motion locus moving along a substantially vertical linear path and in the mean time a boom length is adjusted, so that a loading position of an object can be freely selected.
2. Description of the Related Art
In general, an industrial vehicle is a vehicle used either to transfer powdered materials such as soils or sands or to load objects at an elevated place, which designates heavy equipment such as a skid steer loader, a forklift, etc.
According to this industrial vehicle, front and rear wheels are installed in front and rear of a vehicular body frame. A boom assembly where a working tool such as a bucket or a forked platform is mounted is installed over the vehicular body frame. The boom assembly moves up and down with respect to the vehicular body frame to perform an unloading work.
FIG. 1 is a schematic view showing a working state of a conventional industrial vehicle.
In order for an industrial vehicle 11 to transfer an object 10 from an old place C where the object is originally placed to a new place E, the following work sequence is performed. The object 10 is loaded on a working tool 12 of the vehicle 11 in the old place C. The vehicle 11 is reversed in a direction of a place D and progressed toward the place E. Then, the object 10 is unloaded. Therefore, unnecessary manipulations such as a progressing motion, a reversing motion, etc. of the vehicle are required, thus increasing a working time.
Further, when the conventional industrial vehicle performs the unloading work, a sufficient space where the vehicle can rotate must be secured. However, such a space is not often secured in various industrial sites and warehouses of stores, etc. As shown, when a wall 13 is present in the place D, the vehicle 11 can not reverse in the direction of the place D, so that works, for example, of transferring the object 10 can not be performed. Therefore, it is strongly required that the industrial vehicle can smoothly work in the narrow space.
A four wheel steering system is employed to the steering system of the industrial vehicle in order to efficiently perform works in the narrow space. The four wheel steering system has an advantage in that the vehicle can rotate at a small radius in the narrow space, unlike the two wheel steering system where only the front or rear wheels are steered.
Technologies on the four wheel steering system are disclosed in Korean Utility Model Publication Nos. 1999-41376 and 1998-45500, in which front wheels are steered in the opposite direction to rear wheels. According to this conventional four wheel steering system, front and rear axles to whose opposite ends the front and rear wheels are mounted are installed in front and rear of a vehicular body. Front and rear steering cylinders are installed to be apart from the front and rear axles at a predetermined interval. Tie rods and knuckle arms are coupled on both sides of the front and rear steering cylinders. As a result, as hydraulic pressure is applied to the steering cylinders, the front and rear wheels are steered left and right.
In spite of this configuration, a steering angle of the wheels is limited to a movement distance of the steering cylinder. Thus, in order to change the progress direction of the vehicle, a rotational space sufficient to progress and reverse the vehicle is required. For this reason, there is a problem in that the work is restricted in the narrow space.
Further, technology capable of easily parking a vehicle in a narrow space is disclosed in Korean Patent Registration No. 4310, in which each wheel can be rotated at an angle of 360° in an arbitrary direction by independent operation. Specifically, two warm gears driven by two stepping motors respectively are installed upside wheels. Warms are engaged between the warm gears. The warms are fixed to steering shafts of the wheels, so that each wheel is independently steered. However, in order to steer each wheel, many components such as stepping motors, gear trains, etc. are required to thus cause a complicated configuration. Consequently, there is a problem in that production costs are increased.
Further, in the conventional industrial vehicle, in order to efficiently operate the vehicle, a differential driving unit for differentially driving left and right wheels is mounted. Most differential driving units have a complicated configuration, so that the number of components is increased together with production costs.
In an initial industrial vehicle, a main arm of a boom assembly is rotatably coupled to a single rotational shaft on a vehicular body frame so as to go up and down in a vertical direction. However, there is a problem in that a leading end of a working tool mounted on a front end of the main arm moves in a bow form.
To be specific, in an early stage where the boom assembly begins to go up, the leading end of the working tool moves forward a vehicular body. After the boom assembly passes through a middle point, the leading end of the working tool moves backward. Thus, there is a problem in that a reach, a distance up to the leading end of the working tool, is decreased when the boom assembly goes up at the highest point.
Therefore, when objects are unloaded on a truck using the industrial vehicle, the industrial vehicle must be operated apart from the truck so as to prevent the working tool from collide with the truck in an initial operation period of the working tool. At a moment when the object is unloaded, a series of manipulations, for example, where the industrial vehicle is progressed at a predetermined interval with the working tool located to be sufficiently higher than an upper portion of a rear end of the truck, must be performed. Further, while the boom assembly goes up, the working tool moves forward at a predetermined distance in relation to the vehicular body. For this reason, in a state where the heavy object is loaded on the working tool, there is a danger that a center of gravity of the vehicle moves forward, and thus the vehicle is upset.
As technologies for solving the foregoing problems in the prior art, an industrial vehicle designed so that a leading end of a working tool moves along a linear path in a substantially vertical direction when a boom assembly goes up is disclosed in Korean Patent Publication No. 2001-63039 and U.S. Pat. No. 5,169,278.
According to these technologies, in an early stage where a boom assembly begins to go up, a working tool also goes up in a substantially vertical direction. For this reason, in order for the working tool to avoid colliding with a rear end of, for example, a truck on which objects are loaded, a series manipulations, for example, of reversing an industrial vehicle are not needed. There is no phenomenon that a reach of the boom assembly is greatly varied in forward and backward directions of the industrial vehicle.
However, because the working tool moves in a direction perpendicular to a vehicular body, when the objects are stacked at the innermost portion of the truck or a container, there is a difficulty that the industrial vehicle must move up to the interior of the truck or the container to unload the objects and reverse again.
Therefore, there is a strong demand for technology that a length of the boom assembly of the industrial vehicle can be adjusted and thereby a position of the working tool unloading the objects can be adjusted in the forward and backward directions.
Further, in the conventional industrial vehicle, when the boom assembly goes up and down, a driver or operator must manually manipulate a control lever to horizontally maintain the working tool. Hence, both proficiency capable of manipulating a main arm and the control lever of the working tool and caution are required. Sometimes, it happens that it is difficult to horizontally maintain the working tool to drop the objects. For these reasons, working efficiency is lowered and a danger of safety accident is always present.
Further, in view of nature of a work performed in the narrow space, there is a case that an old place where the objects are originally placed is close to a new place where the objects are to be newly stacked. In this case, when the objects are unloaded using the industrial vehicle, the industrial vehicle must be reversed, rotated, and progressed with the objects loaded on the working tool, and thereby the front of the industrial vehicle must face the new place.
In order to perform the works in the narrow space, the industrial vehicle is designed to have a minimum rotational radius. However, many working environments are so narrow that rotation of the industrial vehicle having a small rotational radius can not be allowed. Therefore, there is a strong demand for technology capable of changing only a direction of the industrial vehicle without rotating the entire industrial vehicle.